Glass fiber cooling means made of palladium

ABSTRACT

A cooling tube assembly for use with a molten glass bushing in the production of glass fibers wherein the cooling tubes of the assembly are fabricated from commercial grade palladium metal and are positioned in a highly corrosive, high-temperature environment.

United States Patent Tilbrook Mar. 7, 1972 [54] GLASS FIBER COOLINGMEANS MADE [56] References Cited F PALLADI M O U UNITED STATES PATENTSm] Invent Kenneth Kansas 3,251,665 /1966 Bour ..65/1 2 x [73] Assignee:Certain-Teed Products Corporation, Ard- 3,210,167 1965 Lacroix et al.more, Pa. 3,345,147 10/l967 Russell [22] Filed: June 15, 1970 3,488,1721/l970 Ahotta et al. ..65/1

[21] Appl. No.: 48,883 Primary Examiner-S. Leon Bashore AssistantExaminer-Robert L. Lindsay, Jr. Related Appllcatlon DamAttorney-Scofield, Kokjer, Scofield & Lowe Continuation of Ser. No.726,799, May 6, 1968, abandoned, which is a division of Ser. No.583,623, Oct. 3, [571 ABSTRACT 1966 3,392,779- A cooling tube assemblyfor use with a molten glass bushing in the production of glass fiberswherein the cooling tubes of the U-S. a embly are fabri ated fromcommercial grade palladium [51] Int. Cl. ..C03b 37/02 mfita] and arepositioned in a highly Corrosive, i h [58] Field of Search ..,.65/l, 2,12, 374; 165/47; mm environment.

1 Claims, 4 Drawing Figures PATENTEDMAR 7 I972 M mull) g IHYENTORKennefh E 77/Ar00k GLASS FIBER COOLING MEANS MADE OF PALLADIUM Thisapplication is a continuation of my Ser. No. 726,799, filed May 6, I968,now abandoned but which was a divisional application of my Ser. No.583,623, filed Oct. 3, I966, now U.S. Pat. No. 3,392,779, issued July16, 1968.

This invention relates to means for cooling molten glass fibers beingdrawn from a bushing and refers more particularly to improvements inliquid carrying cooling tubes adapted for use adjacent the fiber drawingorifices of a bushing containing a supply of molten glass.

The US. Pat. to Russell No. 3,068,670 Apparatus for Production of GlassFibers," issued Dec. 18, I962, shows the use of hollow, liquid carryingfiber cooling tubes associated with a bushing. The same is true ofPhillips, US. Pat. No. 2,632,287, issued Mar. 24, 1953, for Apparatusfor Producing Fibrous Glass.

In the process of attenuating glass fibers, by drawing same fromorifices located in the bottom of a bushing containing a supply ofmolten glass, it is desirable that the viscosity of the glass be low sothat the rate of flow is maximized. Once a fiber has left the orifice,it is desirable that the viscosity thereof be high, so that the fiberwill not break. Inasmuch as viscosity is an inverse function of thetemperature, it is evident that the fiber should be rapidly cooled afterit has left the orifice. The US. Patents to Case 2,955,772, issued Oct.1 l, 1964 Textile Fiber Winder," Higgins, Jr. US. Pat. No. 3,022,020,issued Feb. 20, I962 Fiber Drawing Apparatus and Stephens et al. U.S.Pat. No. 3,268,314 issued Aug. 23, I966 Apparatus For Detecting BreaksDuring Molten Fiber Formation all disclose typical apparatus associatedwith operations involving fibers drawn from bushings.

To most advantageously accomplish the aforementioned immediate coolingof the fibers as they emerge from the bushing, applicant utilizes hollowtubes through which a cooling liquid such as water flows. These tubes,flattened in cross section are positioned closely below and adjacent thebushing lower surface and between sets of the orifices thereof fromwhich the molten glass fibers are drawn. Typically, two rows of bushingorifices are located between each adjacent pair of tubes so that eachnewly formed glass fiber is adjacent to at least one tube and can loseheat to it by radiation. It has been proposed in the art to utilize, asfabrication metals for cooling tubes such as those instantly disclosedand/or solid fin type cooling devices copper, platinum, silver,aluminum, monel, and nickel, as well as alloys of such metals. The arthas alleged that such metals can perform satisfactorily. With respect tohollow, liquid filled cooling tubes, there is little question that theycan successfully perform the cooling function fabricated from any ofthese or other metals. However, corrosion of such liquid carrying metaltubes creates serious problems. In the rigorous environment closely nextthe bushing undersurface, some of the constituents of the molten glassvaporize and later condense on the relatively cold heat exchangesurfaces of the tubes. Among such are fluorine compounds such as calciumand sodium salts which react vigorously with most metals.

As noted, it is also conventional as may be seen in the Russell US.Patent No. 2,908,036, Apparatus for Production of Glass Fibers, issuedOct. 13, I959, to use solid cross section fin constructions as coolingmeans, same positioned closely adjacent and between the bushingorifices. Such fins are connected at one end to a member through whichcooling water passes. The corrosion problem noted above applies both tosuch fins and hollow tubes. However, it should be readily appreciatedthat the effects of corrosion on thin wall tubes are much more drasticthan on a solid fin. The tubes in question typically have a wallthickness of from 0.005 to 0.010 inches, about the same as from one totwo sheets of conventional writing paper. A fin is typically about asthick as the overall width or thickness dimension of the flattened tube,namely, from 0.050 to 0.060 inches. When a portion of the wall of such atube is eaten away by corrosion effects, water may squirt out on the hotbushing and can cause serious damage. When the top of a fin (of anymetal) is eaten away by the same cause, nothing much happens except thatthe cooling area is reduced.

Of course, after a sufficient period of time, even the fins must bereplaced to retain cooling efficiency in the precise zone desired.

Platinum has been proposed and used as the fabricating metal for bothfins and tubes. Although platinum fins and tubes do not corrode, adeposit collects on them which adversely affects heat-transfer capacity.This deposit can easily be removed by washing with plain water. Innormal operation, this is done once every seven to ten days. The greatdrawback to the use of platinum is its high cost, which approximates$1,900.00 per pound ($1,470.00 per cubic inch). It is greatly desirableto provide a suitable substitute for platinum as the fabricating metalliquid-cooled cooling tubes to be used in the virulently corrosiveatmosphere closely adjacent the undersides of glass fiber bushings.

An object of the instant invention is to provide liquidcooled tubes tobe used in association with heated bushings from which glass fibers aredrawn which are formed to the desired minimum total width or thickness,having also the desired thin wall for optimum heat-transfer effects andfurther having complete corrosion resistance, for all practicalpurposes, under the extreme conditions of temperature and corrosiveatmosphere immediately adjacent the heated bushing itself.

Another object of the invention is to provide hollow, liquid carryingcooling tubes of a metal both resistant to corrosion and readily formedor fabricated as a thin wall structure into flattened shape whereby toobtain the maximum heat exchange surface adjacent the fibers being drawnfrom the glass bushing orifices, said tubes fabricated of palladiummetal.

Another object of the invention is to provide flow through cooling tubesof the metal, palladium, which has physical properties adequate andsatisfactory for the purposes required which additionally have as longlife in service operation adjacent a glass bushing as like tubes ofplatinum metal, yet which have a total cost of only l5 percent that ofplatinum tubes.

Another object of the invention is to provide a basic new use andpurpose for the metal palladium in an environment and under conditionswhere such practical commercial use and usefulness are unexpected andunobvious and wherein a great commercial saving is obtainable.

Other objects of the invention will appear in the course of thefollowingdescription thereof.

In the drawings, which form a part of the instant specification and areto be read in conjunction therewith, an embodiment of the invention isshown and, in the various views like numerals are employed to indicatelike parts.

FIG. 1 is a side view of an array of apparatus incorporating a set ofliquid-cooled heat-transfer tubes and adapted to position same below abushing containing molten glass adjacent the bushing orifices from whichglass fibers are drawn, parts of the apparatus cut away to betterillustrate certain details of structure. 7

FIG. 2 is a top plan view of the apparatus seen in FIG. 1, taken alongthe line 22 of FIG. 1 in the direction of the arrows, a portion of thestructure cut away for illustrative purposes.

FIG. 3 is a view taken along the lines 3-3 of FIG. 1 in the direction ofthe arrows.

FIG. 4 is a view taken along the lines 4-4 of FIG. 1 in the direction ofthe arrows.

Referring to the drawings, at 10 is an input water header or manifoldhaving an input hose connection fitting 10a on the top side thereof.Header 10 has a plurality of output spouts or tubes 11 extending out ofone side of the body thereof. Support bars 12 and 13 are fixedlyattached to the opposite ends of header l0 and are removably connectedat their outer ends to elongate side members 14 and 15.

Opposite input header 10 is output header or manifold 16 which hasoutput hose connection fitting 17 on the underside thereof. Outputheader 16 has input flow tubes or spouts 18 entering and connected toone sidewall thereof. Support bars 19 and 20 are fixed to the oppositeends of header 16 and are removably connected at their outer ends toelongate side support and brace members 14 and 15 in the same manner asthe members 12 and 13 on input header l0. Sleeves 21 and 22 are attachedto the output tubes 11 of header and input tubes 18 of header 16,respectively. Headers 10 and 16 and input and output tubes 11 and 18thereof are typically made of stainless steel. Sleeves 21 and 22 arepreferably made of a suitable elastomeric substance such as Tygon.

An array of palladium tubes 23, circular in transverse section at theends thereof and flattened centrally thereof are positioned in parallelorientation between headers 10 and 16, the free ends thereof received insleeves 21 and 22. Said tubes are generally designated 23 and have, asmentioned, circular cross section free ends 2311 and 23b are fixedlyreceived in spacer bars 24 and 25. The latter extend at right angles toside members 14 and and are secured thereto by brackets or clips 26 forbar 24 and 27 for bar 25. Bolts 28 extend downwardly from the undersidecorners of the glass bushing frame, the latter schematically indicatedat 29, same extending through slots or openings 26a and 27a, in clips orbrackets 26 and 27, respectively. Wing nuts 28a on bolts 28 underliebrackets 26 and 27 and support the header-tube array from the bushing. Aseries of set or adjustment screws 30 threadably extend through openings31 in brackets 26 and 27 and fix the vertical distance of the coolingtube support framework below bushing 29. The view of FIG. 2 shows theflattened portions of the palladium tubes positioned a little furtherbelow the orifice nipples 29a of bushing 29 than would generally be thecase, as will be later described.

Spacer bars 24 and 25 rigidly grip the round portions 231: and 23b oftubes 23 adjacent the ends thereof whereby to prevent same from turningand also perform the function of precisely spacing them as desired withrespect to one another and the bushing orifices. Tubes 23 are typicallypositioned so that there are two rows of bushing orifices between eachtube, but may be so positioned as to have one tube on each side of eachrow of bushing orifices. It is not desirable to have more than two rowsof bushing orifices between each pair of tubes as, then, the centralline of fibers being drawn would not have a cooling tube immediatelyadjacent either side thereof. It has been well established that the useof cooling fins or tubes permits a hotter glass temperature in thebushing with the attendant desired reduced viscosity of the glass. Thispermits an increase in through-put rate of the bushing. The chillingaction of the fins or cooling tubes raises the viscosity of each glassmeniscus immediately below the bushing to the point where fiber formingbecomes feasible. The desirability of the flowthrough cooling tubes oversolid cross section fins has clearly been established in that suchpossess a much greater cooling efficiency. There has been demonstratedat least a 100 percent increase in heat pickup. in drawing of glassfibers from bushings under the various conditions of the fiber formingprocess, there occurs lateral motion and whip of the fibers wherebycontact of same with the cooling tubes, or fins, if same are employed,occurs. In a water-cooled tube, the relatively low surface temperatureeliminates the problem of wet-out, a condition where the newly emergentglass fiber would adhere to the cooling fin or tube surface. Thefiberizing rate is typically increased between solid fins and watercooled tubes by from 8 to 10 percent, depending on fiber diameter.

Palladium, the metal which I employ for my liquid cooled tubes is notsatisfactory in contact with molten glass. It lacksv high temperaturetensile strength. It thus cannot perform as an effective resistanceheater for textile fiberizing glasses, e.g., E glass, a calciumborosilicate glass. Thus, palladium cannot be employed in substitutionfor the underplate of the glass melting bushing 29.

ln studying the behavior of solid fin bushing cooling elements, 1 haveobserved that the problem of wet-out" is critical. That is, the problemof the newly emergent glass fibers contacting the said solid coolingelements and adhering thereto. If the fin is hot, then the wet-outproblem is critical. Therefore, for a practical and useable solid fin, acooling device the use of an efficient heat transfer and conductingmetal is required so that the fin itself, in the zone of the bushingorifices, will be continuously maintained at a low enough temperature toavoid wet-out. On a practical basis, I have discovered that silver,copper, and in some cases, aluminum, have sufficient heat conductivityto be employed as the fabricating element for solid fins. However, steelalloys, platinum, and most importantly, palladium, l have found to haveinsufficient thermal conductivity to warrant the practical, commercialuse of same in solid fin form. Thus, for example, at 212 F., platinumand palladium have conductivities of only 0.173 and 0.168 calories perdegree centigrade per second, respectively. Further with respect topalladium metal as useable in the construction of solid fin coolingelements, because of the relatively low strength of palladium atelevated temperatures, with its low thermal conductivity, the problem ofstructural distortion is present.

Palladium, Pd, is chemical element no. 46, a white and very ductilemetal which may be worked down cold to thin foil and fine wire. Becauseof its softness, it is often alloyed with other precious or base metalsto increase its hardness and tensile strength. The literature indicatesthat the most important use of pure palladium is in low currentelectrical contacts, especially in telephone equipment. Palladiumsupported on carbon or alumina is used as a catalyst in chemicalreactions. Palladium alloyed with ruthenium has the proper hardnessforjewelry. It is unique in the number of metals with which it can bealloyed and is noted as generally producing ductile solid solutions.Alloyed with other precious and base metals, palladium is also used fordental purposes and special resistance wires.

The atomic weight of palladium is 106.7. lt hasa density at 20 C. of12.00 grams per cubic centimeter. The melting point is l,552 C. A thinoxide surface film is formed on palladium when it is heated in air to360-800 C. but same decomposes at higher temperatures to leave the metalbright. Palladium in ordinary atmospheres is recited as resistant totarnish, but will tarnish slightly in outdoor exposures insulphur-contaminated atmospheres. The literature notes that the metal isreadily attacked by nitric acid, ferric chloride, and by moist chlorine,bromine and iodine. I employ, preferably, commercially pure palladium inmy bushing cooling tubes. The common level of purity is 99.85 percentand the minimum commercial limit is 99.5 percent according to the MetalsHandbook, 8th edition, American Society for Metals, 1961. As stated inthe latter reference, page 1,180, palladium, in contrast to platinum, isnot resistant to highly oxidizing chemical environments. It is regardedas being, in general, less resistant to corrosionthan platinum.Palladium has a density 0.6 that of platinum and a cost 0.25 per poundthat of platinum. Thus, tubes of the character described, formed ofpalladium, cost only 15 percent as much as platinum.

No internal cleaning is required, generally speaking, of palladium tubesfabricated according to the specifications to be described. Undercertain circumstances, depending upon the source of cooling water,filters may desirably be employed in view of the centrally restrictedorifices of the tubes. Thus, the tubes are very substantially cheaperthan platinum tubes in initial installation, they are quickly andreadily removable for external cleaning, weekly, and may be replacedwithin 10 minutes. The (presumed fluoride) deposits which build up onthe outsides of the tubes may be removed by washing with water. Thewater flow through the cooling tubes for one bushing of 204 orifices isapproximately 1.7 gallons per minute.

As may be seen in the drawings, the flattened central portions of thetubes run vertically. Typically, the upper edge of the tube ispositioned from approximately one thirty-second of an inch above thelower orifice tip to three thirty-seconds of an inch below same when thebushing is in cold condition. The external vertical height of thetypical flattened central portion of a palladium tube is 0.375 inches. Atypical central external width or thickness dimension of same is 0.060inches. A typical side wall thickness of a palladium tube would be 0.010inches. The round end section outer diameter of the tubes illustrated istypically 0.030. Such a tube would typically be positioned between twolines of orifice nipples on the underside of the bushing, the lines 0.30inches apart on centers. The nipples themselves are typically sized0.150 inches at their emergence from the bushing lower surface and 0.112 inches at the lower ends thereof. These values may vary somewhat indifferent types of bushing construction. This gives a clearance ofapproximately 0.064 on each side of the palladium tube flattened centersection from the bushing orifice nipple walls.

There must be a positive water flow through the tubes, that is, if steamwere to be generated therein, the tubes would be distorted. Typically,input water from 55 to 100 F. may be employed and a 3 to 5 F. change intemperature may be expected, at the volume flow-through rate aboveindicated. The vertical height of the flattened tube portions is limitedsomewhat by mechanical interference factors in the fiberizing process.With the height of the flattened tube portion of the magnitudedescribed, the width as described and the position of the top edge ofthe flattened portion as also indicated, the instant tube constructionis not obstructive with respect to the fiberizing process. It should benoted, that, in like circumstances, a 0.060 inch thickness solid finwould tend to wet-out unless copper or silver, that is, highconductivity materials, are used. The cost of palladium is approximately$495.00 per pound or $215.00 per cubic inch.

it should be noted that certain other readily available materials, whichare generally considered considerably resistant to both corrosion andhigh temperatures, as well as ad vantageous from a price standpoint,have proved to be completely inadequate with respect to corrosionresistance. Thus, Monel 400 a (nickel-copper alloy made by InternationalNickel Company) with an approximate cost of $4.00 per pound andl-lasteloy C (a nickel-molybdenum-chromium-iron alloy made by UnionCarbide) with an approximate cost of $10.00 per pound were unable towithstand the corrosive atmosphere of the bushing underside. in fact,the latter two materials proved to corrode badly after only a few daysof service. These, being low conductivity materials, were tested in tubeform.

Thus it is seen that there has been provided cooling means comprisinghollow liquid-filled tubes fabricated of palladium metal which willperform all of the desired functions of solid fin bushing orificecoolers utilizing metals of high conductivity, including temperaturecontrol adjacent the bushing orifices, reduction of air turbulencetherearound and, further, accomplish a marked increase in bushing outputover the said solid fin elements. Despite the known poorer corrosionresistance of palladium with respect to platinum, the relative strengthdeficiency of palladium compared to same, the relatively poor heatconductivity of palladium compared to such metals as silver and copperand the discovered lack of utility of palladium in use as a solidcooling fin, l have been able to demonstrate the utility of said metalin fabrication of and use as bushing cooling elements by employment ofsame in hollow, liquid-filled tube form. This demonstration is bothunexpected and greatly advantageous from a commercial and practicalstandpoint.

The tubes are formed only centrally flat as the longer the flat sectionthe higher chance of cracks and resultant corrosion. Further, utilizingthe resilient sleeve connection to the header, which permits angularadjustment of the tube flats, with respect to one another and alsopermits the ready replacement of individual tubes, the round end sectionis far preferable. Removable tubes permit one inventory of tubes for avariety of bushings.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure.

It will be understood that certain features and subcombinations are ofutility and may be er nployled wjthout reference to other features andsubcombinations. his is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

I claim:

1. A bushing cooling assembly comprising:

a bushing containing a supply of molten glass and having a plurality oforifices in the under side thereof from which glass fibers may be drawn,

said orifices being arranged in at least two parallel rows, and

a hollow elongate bushing cooling tube positioned closely below andbetween the said rows of fiber drawing orifices,

said tube formed of palladium metal of not less than 99.5 percent purityand flattened centrally of the ends thereof,

said tube carrying a liquid cooling medium centrally thereof for heatexchange purposes with the zone exterior thereof through the outersurface thereof,

said tube positioned in the highly corrosive, high-temperatureenvironment immediately below said bushing closely adjacent to the fiberdrawing orifices thereof.

